Purpose
To assess the impact of obesity and population attributes on the circadian pattern of cardiac autonomic modulation (CAM) in a population-based sample of adolescents.
Methods
We used data from 421 adolescents who completed the follow-up exam in the Penn State Children Cohort (PSCC) study. CAM was assessed by heart rate variability (HRV) analysis of beat-to-beat normal R-R intervals from a 24-hour ECG, on a 30-minute basis. The HRV indices included frequency domain (HF, LF, and LF/HF ratio), and time domain (SDNN, RMSSD, and HR) variables. Nonlinear mixed-effects models were used to calculate a cosine periodical curve, each has three parameters that quantify its circadian: M (mean levels of the HRV variables), Â (amplitude of the oscillation), and θ (the timing of the highest oscillation).
Results
The mean(SD) age was 16.9(2.2)yrs, with 54% male and 77% white. The mean BMI percentile is 66; with 16% obese (BMI percentile ≥95). Overall, HF (a marker of parasympathetic modulation) gradually increases from late afternoon reaching the peak amplitude around 3:00AM, and then decreasing throughout the daytime until late afternoon. In contrast, obesity had adverse effects on all circadian parameters. The age, sex and race showed varying differences on the CAM circadian parameters. The adjusted means (95%Cls) of M, Â, and θ for HF where 5.99(5.79–6.19), 0.77(0.66–0.89), 3:15(2:15–4:15)AM, and 6.21(6.13–6.29), 0.66(0.61–0.70), 2:45(2:30–3:15)AM for obese and non-obese, respectively.
Conclusion
Circadian pattern of CAM can be quantified by the three cosine parameters. Obesity is associated with lower HRV even in young individuals like children/adolescents.